This invention relates generally to electronically controlled fuel injection systems and, more particularly, to a method and apparatus for delivering multiple fuel injections to the cylinder of an internal combustion engine during a fuel injection event based upon engine operating conditions and determining when the fuel injector device should transition between injection waveforms providing different numbers of fuel injections during a particular injection event.
Electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired injection rate including the number of injections in each injection event as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are increasingly becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Tailoring the number of injections and the injection rate of fuel to a combustion chamber, as well as the quantity and timing of such fuel injection is one way in which to control emissions and meet such emission standards. As a result, multi-shot injection techniques have been utilized to modify the bum characteristics of the combustion process in an attempt to reduce emission and noise levels. Multi-shot fuel injection typically involves splitting the total fuel delivery to the cylinder during a particular injection event into a plurality of separate fuel injection shots such as, for example, a pilot injection shot, a main injection shot, and an anchor injection shot. However, at different engine operating conditions, it may be necessary to use different injection strategies, that is, a different number of fuel shots, in order to achieve both desired engine operation and emissions control. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four stroke engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
As a result, based upon varying operating conditions, the number of fuel shots, injection timing, pressure and quantity of fuel may change in order to achieve desired emissions and desired fuel consumption. This means that different injection waveform types are preferrably used based upon engine speed and engine load. In some systems, the fuel injectors used have been somewhat limited as to the particular types of injection current waveforms which could be utilized. As a result, problems such as injecting fuel too rapidly within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect emission outputs and fuel economy.
In a system in which multiple injections and different injection waveforms are achievable, it has been determined that transfer from one type of waveform to another type of waveform must be better controlled under certain circumstances in order to prevent excessive noise and unnecessary repeated transition back and forth between two different waveform types causing decreased engine and emissions performance, and potentially unstable engine operation. It is therefore desirable to control and deliver any number of separate fuel injection shots to a particular cylinder during a particular injection event so as to minimize emissions and fuel consumption based upon the operating conditions of the engine and to provide a smoother, more controlled and stable transition between different waveform types.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, there is disclosed an electronically controlled fuel injection system which is capable of delivering multiple fuel injection shots to a particular cylinder of an internal combustion engine during a single injection event. The system includes at least one fuel injecting device operable to deliver a plurality of fuel injection shots, and a controller which is operable to determine the active injection waveform or number of fuel shots to be delivered during the injection events based upon engine operating conditions.
In a preferred embodiment, the controller is operable to determine a potential injection waveform based on a lookup table or map which selects the potential waveform based upon load and engine speed and engine load. The controller is also operable to set single check fuel hysteresis values and engine speed hysteresis values, and thereafter determine both a fuel change and an engine speed change. The controller then compares the fuel hysteresis values with the fuel change and the engine speed hysteresis values with the engine speed change. If the fuel change is greater than the fuel hysteresis values, and the engine speed change is also greater than the engine speed hysteresis values, the controller will change the active waveform to the potential waveform and store the current fuel and engine speed values. Alternatively, if the fuel change is consistently greater than a loop fuel hysteresis, which loop fuel hysteresis has a different band than the single check fuel hysteresis, for greater than a selected period of time, then the active waveform will be changed to the potential waveform. This is accomplished using a loop counter which is reset if the potential waveform equals the active waveform or the fuel change is less than loop fuel hysteresis values. Thus, the fuel change must be greater than the loop fuel hysteresis values continuously throughout the selected time period.
In another aspect of the present invention, a computer readable medium contains instructions for controlling the fuel injection control system to transition from one waveform to another waveform. The instructions determine if the fuel change and engine speed change are greater than the fuel hysteresis and the engine speed hysteresis, respectively. The instructions also repeatedly compare the fuel change to the loop fuel hysteresis values, and if the fuel change is consistently greater than or equal to the loop fuel hysteresis values for more than approximately 3.8 seconds, the active waveform is changed to the potential waveform.
In still another aspect of the present invention, a method is described for controlling a fuel injection control system to transition from one waveform to another. The method comprises setting single check fuel hysteresis values, loop fuel hysteresis values, and engine speed hysteresis values. A potential waveform is determined from a lookup table or map, and a single check fuel change, an engine speed change, and a loop fuel value change are determined by comparing current fuel and engine speed values with previous fuel and engine speed values. If both the single check fuel change and engine speed change are greater than the respective hysteresis values in a single check, the active waveform is changed to the potential waveform. Additionally or alternatively, if the loop fuel value change is greater than the loop fuel hysteresis values for a repeated number of comparisons, the active waveform is changed to the potential waveform.